222 ISSN 0097-8078, Water Resources, 2018, Vol. 45, No. 2, pp. 222–230. © Pleiades Publishing, Ltd., 2018. Original Russian Text © V.N. Egorov, S.B. Gulin, L.V. Malakhova, N.Yu. Mirzoeva, V.N. Popovichev, N.N. Tereshchenko, G.E. Lazorenko, O.V. Plotitsina, T.V. Malakhova, V.Yu. Proskurnin, I.G. Sidorov, A.P. Stetsyuk, L.V. Gulina, 2018, published in Vodnye Resursy, 2018, Vol. 45, No. 2. Rating Water Quality in Sevastopol Bay by the Fluxes of Pollutant Deposition in Bottom Sediments V. N. Egorov*, S. B. Gulin, L. V. Malakhova, N. Yu. Mirzoeva, V. N. Popovichev, N. N. Tereshchenko, G. E. Lazorenko, O. V. Plotitsina, T. V. Malakhova, V. Yu. Proskurnin, I. G. Sidorov, A. P. Stetsyuk, and L. V. Gulina Kovalevskii Institute of Marine Biological Research, Sevastopol, 299011 Russia *e-mail: egorov.ibss@yandex.ru Received May 13, 2015; in final form, January 26, 2017 Abstract⎯Sevastopol Bay is used as an example for the development of criteria for rating anthropogenic impact by elimination fluxes from the water area of post-Chernobyl ( 90 Sr, 137 Cs, 239,240 Pu) and natural ( 210 Pо) radionuclides, as well as mercury and organochlorine compounds. The differentiation of the bay water area into zones with different biogeochemical conditions and the balance approach to interpreting field observa- tion data were used to assess the conditioning capacity of Sevastopol Bay ecosystem for conservative radioac- tive and chemical substances by elimination fluxes of pollutants into aqueous depot, which is the open part of the Black Sea and into the geological depot, i.e., its bottom sediment stratum. Keywords: Sevastopol Bay, bottom sediments, post-Chernobyl radionuclides, mercury, organochlorine com- pounds, deposition fluxes DOI: 10.1134/S0097807818020069 INTRODUCTION Sevastopol Bay is a water area of higher environ- mental risk because of its limited water exchange with outer harbor resulting from the construction of pro- tection piers, high technogenic activity in the coastal area, wastewater discharges [9], and pollutant inputs with the Chernaya R. water [8]. The need to control the ecological state of the bay requires the regulation of the equilibrium between the use and reproduction of the quality of its water resources. The objective of the study was to develop criteria for rating the anthropogenic impact on Sevastopol Bay water area by the deposition fluxes into its bottom sediment of post-Chernobyl ( 90 Sr, 137 Cs, and 239,240 Pu) and natural ( 210 Po) radionuclides, as well as mercury and chlorinated hydrocarbons under current condi- tions of natural biogeochemical cycles, through which its water conditioning is taking place. MATERIALS AND METHODS The study was carried out in Sevastopol Bay and, for comparison, in the outer harbor of Sevastopol. The zoning of the bay water area by hydrodynamic, hydro- chemical, and morphological characteristics (Fig. 1) has been carried out in accordance with criteria described in [5, 11]. The concentrations of 90 Sr, 137 Cs, 239,240 Pu, 210 Po, Hg and organochlorine compounds (OCC) were measured by standard procedures [6, 10, 12]. To date the bottom sediments in the study areas, soil core columns were taken and separated into layers 5–10 mm in thickness; the concentrations of 137 Cs or 90 Sr were measured in each layer, depending on which radiotracer has been chosen. The data samples thus obtained were compared to identify layers with maxi- mal radionuclide concentrations. The formation age of these layers corresponded to periods of maximal fallout of fission radionuclides after global nuclear weapon tests in the atmosphere, on land surface, and in oceans in 1962, as well as the result of the release of post-Chernobyl radionuclides into the environment in 1986. The rate of sedimentation was evaluated by the distance between layers with peak concentration val- ues of fission radionuclides both between one another and from the surface layer in the core columns. A cor- rection was introduced to account for changes in soil density in bottom sediment columns [1, 3, 7]. RESULTS AND DISCUSSION The radioactive and chemical substances under consideration are conservative pollutants of the marine environment. Therefore, the main self-purifi- cation mechanisms of the marine environment involve only the reduction of their concentrations in water because of their migration into nearby water areas and sedimentation elimination into bottom sediments. HYDROCHEMISTRY, HYDROBIOLOGY, ENVIRONMENTAL ASPECTS